1. Field of the Invention
The invention relates to an apparatus and a method for switching real-time media streams from one or multiple sources to one or multiple sinks. Furthermore, the invention relates to a corresponding computer program.
2. Present State of the Art
In the area of professional TV studios it is common to connect sources of real-time media flows, e.g. TV cameras producing real-time video streams, and corresponding sinks, e.g. suitable studio monitors or digital editing suites, by a serial, digital interface, which is called “Serial Digital Interface (SDI)” in English. The SDI-interface allows for a transmission of uncompressed, unencrypted digital video streams (and optionally of embedded time code streams and/or audio streams) through coaxial cables or optical wave guides and comprises a whole family of standards specified by the SMPTE (English “Society of Motion Pictures and Television Engineers”) for different video formats and bit rates respectively. Thus, the standard SMPTE 259M (English “Standard Definition”), also known as SD-SDI, defines for example the digital transmission of PAL video signals (English “Phase Alternating Line”) in the 576i format (English “interlaced”) with a bit rate of 270 Mbit/s and the standard SMPTE 344M (English “Enhanced Definition”), also known as ED-SDI, allows for a digital transmission of PAL video signals in the 576p format (English “progressive”) with a bit rate of 540 Mbit/s. For high-resolution HDTV applications (English “High Definition Television”) the standard SMPTE 292M, also known as HD SDI allows for a digital transmission of video signals in the 720p or 1080i format with bit rates of 1.485 Gbit/s and 1.485/1.001 Gbit/s. For even bigger video formats, e.g. in the area of digital cinema or 3D-cinema, suitable standards with correspondingly even higher bit rates are available as well. Examples therefor are the standard SMPTE 372M, also known as Dual-Link HD-SDI, and the standard SMPTE 424M (English “Third Generation”), also termed 3G-SDI.
In order to switch real-time media streams between sources and sinks so-called SDI crossbars are generally used in television studio studio engineering. These devices feature source and sink ports for digital video streams for different SDI formats, e.g. SD-SDI, HD-SDI and 3G-SDI, depending on their equipment components, and allow for a transparent switching of the sinks to the sources, i.e. it is ensured that switching occurs between two chronologically sequent access units, i.e., for instance between two chronologically to subsequent frames with digital video streams. The switching operation occurs for this chronologically predetermined switching points or within predetermined switching ranges respectively, which are defined within the directive SMPTE RP168 (English title “Definition of Vertical Interval Switching Point for Synchronous Video Switching”) for video streams in the SDI format, for example.
However, the transmission of real-time media streams by the SDI interface and the switching by means of correspondent SDI crossbars in the television studio has the disadvantage that the studio technology necessary for this is expensive and the maximum cable length of the coaxial cables generally used for the transmission is limited. Therefore, it is desirable for the future not least because of economical aspects to change the serial, digital infra structure used in the television studios to a packet-switched infrastructure, i.e., e.g. IP-based (English “Internet Protocol”), as it is already widely used in recent computer network technology. Such a packet-based solution could be cheaper in the long run than the “special” solution used in studios now, and it could be used for transmission of other formats, e.g. compressed video formats such as JPEG200 or container formats such as MXF (English “Material eXchange Format”) in addition to the transmission of digital video streams in the SDI format. Furthermore, the integration of software-based image processing and corresponding storage media would be easier as well within a packet-switched infrastructure.
While there are already existing solutions for the transmission of real-time media streams by IP-based networks with the SMPTE 2022 standard family and the standard SMPTE 2022-6 (English title “High Bit Rate Media Transport over IP Networks” (HBRMT)) in particular allows for the transmission of digital video streams provided in the SDI format by IP-based networks (also called “SDI over IP”), so far there is a lack of suitable solutions for switching such signals transparently, i.e. between two chronologically sequent access units, in a “packet-switched world”.